an enclosed chamber in which heat is produced to heat buildings, destroy refuse, smelt or refine ores, etc.
source: WordNet 3.0
An inclosed place in which heat is produced by the combustion of fuel, as for reducing ores or melting metals, for warming a house, for baking pottery, etc.; as, an iron furnace; a hot-air furnace; a glass furnace; a boiler furnace, etc.
source: Webster 1913
To throw out, or exhale, as from a furnace; also, to put into a furnace.